In order to assess the clinical and pathologic significance of the immunologic characterization of human malignant lymphomas, biopsy tissues are obtained from patients referred to the Clinical Center for treatment and/or diagnosis. Biopsies are obtained with patient permission prior to therapy and processed in the Hematopathology Section. Paraffin blocks from biopsies performed outside the NIH are obtained for immunophenotypic characterization. The neoplastic cells are characterized as to their origin from T cells, B cells, or histiocytes, and in addition can be identified as belonging to specific developmental and functional subpopulations. Immunophenotypic data are correlated with histologic and clinical findings, with the goal of defining distinctive clinicopathologic entities. The relevance of immunophenotype as correlated with response to therapy is explored. Immunophenotypic and morphologic data are correlated with molecular and cytogenetic findings, to define the pathogenesis of disease entities. This information is used to define new clinicopathologic entities, and to further refine the definition of currently recognized diseases. It is also used as a basis for immunotherapy, either alone or in concert with conventional chemotherapy and radiotherapy.